U0100

DTC U0100-U0299

CIRCUIT DESCRIPTION
Modules connected to the high speed GMLAN serial data circuits monitor for serial data communications during normal vehicle operation. Operating information and commands are exchanged among the modules. The modules have prerecorded information about what messages are needed to be exchanged on the serial data circuits, for each virtual network. The messages are supervised; also, some periodic messages are used by the receiver module as an availability indication of the transmitter module. The supervision time-out period is 250 ms. Each message contains the identification number of the transmitter module.

DTC DESCRIPTORS
This diagnostic procedure supports the following DTCs:
- DTC U0100 Lost Communication With Engine Control Module (ECM) or lost communication with Powertrain Control Module (PCM)
- DTC U0101 Lost Communication With Transmission Control Module (TCM)
- DTC U0121 Lost Communication With Electronic Brake Control Module (EBCM)
- DTC U0140 Lost Communication With Body Control Module (BCM)
- DTC U0126 Lost communication with Power Steering Control Module (PSCM)




This vehicle has DTCs which include DTC Symptoms. For more information on DTC Symptoms refer to DTC Symptom Description. Symptoms - Vehicle

CONDITIONS FOR RUNNING THE DTCs
- Voltage supplied to the modules is in the normal operating voltage range.
- The vehicle power mode requires serial data communication to occur.
- The DTC U0001 does not have a current status.

CONDITIONS FOR SETTING THE DTC
A supervised periodic message that includes the transmitter module availability has not been received.

ACTION TAKEN WHEN THE DTC SETS
The module uses a default value for the missing parameter.

CONDITIONS FOR CLEARING THE DTC
- A current DTC clears when the malfunction is no longer present.
- A history DTC clears when the module ignition cycle counter reaches the reset threshold, without a repeat of the malfunction.

DIAGNOSTIC AIDS
- A poor connection at the inoperative module may cause this code to set.
- An improperly powered module may cause this code to set.

TEST DESCRIPTION

Step 1 - Step 9:

Step 10 - Step 18:

The numbers below refer to the step numbers on the diagnostic table.
3. The scan tool communicate with OnStar(R) via class 2, so for high speed GMLAN data link diagnostic the OnStar(R) will not be considered.
15. The module which was not communicating due to an open in the GMLAN serial data circuits may have set Loss of Communication DTCs for those modules that it was monitoring.
17. The modules which can communicate indicate the module which cannot communicate. You must clear the DTC from these modules to avoid future misdiagnosis.